Multilayer stent

ABSTRACT

A composite stent having a substrate tube made of stainless steel, a nickel-cobalt-chromium-molybdenum alloy, or chonichrome with at least one metal cladding tube is disclosed. Specifically, the substrate tube is placed within a metal cladding tube made of platinum, gold, tantalum, tungsten, platinum-iridium, palladium, or nickel-titanium, preferably with an interference fit therebetween. The composite, laminate tube then undergoes a series of rolling or cold drawing processes interspersed with heat treating to release built up stresses. When the final diameter of the laminate tube is reached, the cladding has been laminated to the exterior of the substrate tube by a bond generated from the rolling and/or cold drawing operations. The finished laminate tube is then cut by laser cutting or chemical etching to form a suitable stent pattern.

This is a divisional application of copending parent application havingU.S. Ser. No. 09/270,403 filed Mar. 16, 1999, the contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to expandable intraluminal vasculardevices, generally referred to as stents. More precisely, the presentinvention is directed to stents that have a metallic cladding forimproved expansion characteristics and radiopacity.

Stents are used to maintain patency of vessels in the body, such as apatient's arteries. A variety of delivery systems have been devised thatfacilitate the placement and deployment of stents. The stent isinitially manipulated while in its contracted or unexpanded state,wherein its reduced diameter more readily allows it to be introducedinto the body lumen, such as a coronary artery, and maneuvered into thetarget site where a lesion has been dilated. Once at the target site,the stent is expanded into the vessel wall to allow fluid to flowthrough the stent, thus performing a scaffolding function. Stents areusually mounted on balloon catheters and advanced to a lesion site byadvancing the catheter. At the site, the stent is expanded by inflatingthe balloon on which the stent is mounted. Deflation of the balloon andremoval of the catheter leave the stent implanted in the vessel in anexpanded state. It is also possible to dilate a vascular lesion anddeploy a stent at the same time using the same expandable member orinflatable balloon. This variation of the procedure described aboveobviates the need for a separate balloon dilation catheter and stentdeployment catheter.

Stents are typically formed from biocompatible metals such as stainlesssteel, nickel-titanium, tantalum, and the like, to provide sufficienthoop strength to perform the scaffolding function of holding thepatient's vessel open. Also, stents have minimal wall thickness in orderto minimize blood flow blockage. But stents can sometimes causecomplications including thrombosis, and neointimal hyperplasia byinducement of smooth muscle cell proliferation at the site ofimplantation of the stent. Such stents typically also do not provide fordelivery of localized therapeutic pharmacological treatment of a bloodvessel at the location being treated with the stent, which can be usefulfor overcoming such problems.

In the evolution of stents, there have been developments in the field ofstents coated with a layer of polymers. The polymeric materials aretypically capable of absorbing and releasing therapeutic drugs. Examplesof such stents are disclosed in U.S. Pat. No. 5,443,358 to Eury; U.S.Pat. No. 5,632,840 to Campbell; U.S. Ser. No. 08/842,660, filed Apr. 15,1997, by J. Yan; and U.S. Ser. No. 08/837,993, filed Apr. 15, 1997, byJ. Yan.

Aside from coated stents, there have been developments in the field ofmultilayer grafts. An example of a multilayer graft is disclosed in U.S.Pat. No. 4,743,252 to Martin, Jr. et al. Martin et al. shows a compositegraft having a porous wall structure to permit ingrowth, which graftincludes a generally non-porous, polymeric membrane in the wall toprevent substantial fluid passage therethrough so as to provide animplantable porous graft that does not require preclotting prior toimplantation. Grafts are known which have multiple layers for strengthreinforcement. For example, U.S. Pat. No. 5,282,860 to Matsuno et al.discloses a stent tube comprising an inner tube and an outerpolyethylene tube with a reinforcing braided member fitted between theinner tube and the outer tube. The inner tube is made of afluorine-based resin.

U.S. Pat. No. 5,084,065 to Weldon et al. discloses a reinforced graftassembly made from a vascular graft component and a reinforcing sleevecomponent. The reinforcing sleeve component may include one or morelayers. The second component of the two component system includes thereinforcing sleeve component. Like the graft component, the reinforcingcomponent includes a porous surface and a porous subsurface.Specifically, the reinforcing sleeve component includes multiple layersformed from synthetic, biologic, or biosynthetic and generallybiocompatible materials. These materials are typically biocompatiblepolyurethane or similar polymers.

Despite progress in the art, there is presently no stent available thathas a metallic cladding for improved strength reinforcement, expansioncharacteristics and radiopacity. Therefore, there is a need for such amultilayer metallic clad or laminate stent.

SUMMARY OF THE INVENTION

The present invention is directed to a multilayer intracorporeal device,specifically a multilayer or laminate stent that has a metallicsubstrate and at least one layer of metallic cladding. The cladding isgenerally joined to the substrate under high pressure resulting in astructure that resists separation or delamination under normal stress.The cladding metal and the base or substrate material form a bondbetween them during a deep drawing, cold drawing, or co-drawing on amandrel process. The method of combining two or more layers of differentmaterials allows for the combination of desirable properties of thosematerials. Typical material properties to be considered for stent designand performance include strength, ductility, and radiopacity. Forexample, a substrate layer material may be chosen for its strength, afirst cladding material chosen for its ductility, and a second claddingmaterial chosen for its radiopacity.

The present invention provides a method of fabricating a stent forimplantation within a body lumen, comprising the steps of providing asubstrate tube having an outside surface and an inside surface;disposing a first cladding tube about the substrate tube, wherein thefirst cladding tube includes a metal; joining the first cladding tube tothe outside surface of the substrate tube to form a laminate tube; andforming a stent pattern in the laminate tube to provide for expansion ofthe stent. In a preferred embodiment, the substrate tube includes ametal selected from the group consisting of stainless steel, anickel-cobalt-chromium-molybdenum alloy, or chonichrome; and the firstcladding tube includes a radiopaque metal, preferably selected from thegroup consisting of platinum, gold, tantalum, tungsten, platinum-10%iridium, or palladium. It may also be desirable to have a substrate tubeof a psuedoelastic alloy such as NiTi. A substrate tube from such analloy can provide mechanical characteristics which facilitate expansionof a stent within a patient's vessels and minimize trauma to thevessels, particularly in indications such as carotid artery treatment.

Joining the first cladding tube to the outside surface of the substratetube can include rolling and drawing the laminate tube to bond or securethe first cladding tube to the substrate tube. This process is known inthe art as deep drawing, cold drawing, or co-drawing on a mandrel.Concurrent or in series with the cold drawing process, the laminate tubecan be heat treated or annealed to release stress build-up from the coldworking. The bond between the substrate tube and the first cladding tubecan be mechanical in whole or in part.

In an alternative method, the present invention further includesdisposing a second cladding tube about the first cladding tube; andjoining the second cladding tube to the first cladding tube. As aresult, the finished stent has two cladding layers laminated on thetubular substrate. Typically, the second cladding layer will be made ofa radiopaque metal, preferably including a metal selected from the groupconsisting of platinum, gold, tantalum, tungsten, platinum-iridium, orpalladium. A preferred platinum-iridium alloy is a platinum-10%iridiumalloy.

The present invention further contemplates a device which is preferablyproduced by the above methods, i.e. a stent for implantation within abody lumen having a substrate tube with an exterior surface; a metalliccladding bonded under pressure about the exterior surface of thesubstrate tube; and a stent pattern formed in the substrate tube and themetallic cladding. In a preferred embodiment, the cladding includes aradiopaque metal, preferably selected from the group consisting ofplatinum, gold, tantalum, tungsten, platinum-iridium, or palladium.Furthermore, the substrate tube generally includes a metal selected fromthe group consisting of stainless steel, anickel-cobalt-chromium-molybdenum alloy, or chonichrome. The substratetube can also include a superelastic or superelastic alloy such as NiTi.

In particular, it has been found that for the substrate tube, materialssuch as 316L stainless steel, nickel-cobalt-chromium-molybdenum alloyssuch as MP35N, or cobalt-chromium-tungsten-nickel-iron alloys such asL605, (chonichrome) are preferable. For the cladding tube, it has beenfound that platinum, gold, tantalum, tungsten, platinum-10%iridium, orpalladium are preferred. Each of the cladding material adds to theperformance of the finished laminate tube which would otherwise not bepossible with a pure 316L stainless steel, MP35N, or chonichrome tubealone. Another benefit of the present invention is that the metalcladded stent can have a desired amount of radiopacity. Indeed, usingcladding tubes made of radiopaque alloys or metals such as platinum,gold, tantalum, or platinum-iridium increases the radiopacity of thestent to assist the cardiologist in tracking the stent duringimplantation.

The present invention can additionally benefit from use of a substrateor cladding tube made from nickel-titanium, which is a shape memoryalloy which can exhibit superelastic properties. With a higherdeformation rate due to a nickel-titanium cladding tube, the laminatestent eliminates the need for higher pressure balloons and as a result,the risk of injury to the vessel walls is reduced. The nickel-titaniumeases the expansion of the stent in normal temperatures and contractionin relatively elevated temperatures. Where a superelastic alloy such asNiTi is used as a cladding layer in combination with a non-radiopaquehigh strength alloy substrate such as stainless steel, MP35N or L605, itis generally preferred to include a second cladding layer or tube of aradiopaque metal such as those described above. In this way, the desiredmechanical characteristics of the stent can be achieved with theappropriate combination of substrate and first cladding materials, andradiopacity is added to the stent by the second cladding layer or tube.

These and other advantages of the present invention will become apparentfrom the following detailed description thereof when taken inconjunction with the accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a preferred embodiment stent with atubular cladding mounted on a mandrel, and undergoing compressionapplied by an external roller.

FIG. 2 is a perspective view of a deep drawing operation showing thepresent invention stent prior to passing through a die.

FIG. 3 is a perspective view of a preferred embodiment metallic cladstent having struts formed therein.

FIG. 4 is a perspective view of an alternative embodiment stent havingmultiple cladding layers with the stent struts formed therein.

FIG. 5 is an elevational view in partial section of a delivery catheterwithin an artery with a laminate stent having features of the inventiondisposed about the delivery catheter.

FIG. 6 is a perspective view of a laminate stent having features of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view of a preferred embodiment of a laminatetube having features of the present invention. As seen in thissimplified view, the present invention contemplates creation of laminatetube 10 by joining metal cladding tube 12 to an exterior surface ofsubstrate tube 14. Fundamental to this joining process is first definingthe initial diameters of metal cladding tube 12, which should already bein a tubular configuration as seen in FIG. 1, and of substrate tube 14.Tubes 12, 14 can be made by conventional fabrication processes, such asdrawing, rolling sheet stock and welding the seam, etc. During thesepreliminary steps, the diameters and wall thickness of tubes 12 and 14are selected and set.

In the preferred embodiment of the present invention, there should be aninterference fit between the outside diameter of substrate tube 14 andthe inside diameter of metal cladding tube 12. The interference fitprevents unwanted, relative shifting between substrate tube 14 and theconcentrically disposed cladding tube 12. It is further preferable thatthe wall thickness of substrate tube 14 be greater than the wallthickness of metal cladding tube 12. The initial wall thicknesses can beimportant, because the present invention processes encompass aco-drawing or cold drawing operation that reduces the diameter and wallthickness of each tube while increasing its length. To maintaincontinuous contact at the interface between the interior of metalcladding tube 12 and the exterior of substrate tube 14, it is preferablethat the initial wall thicknesses of the respective parts be asdescribed above.

The volumes of metal cladding tube 12 and substrate tube 14 areconserved throughout the various cold drawing stages of diameterreduction. Because the outer tube has a larger surface area than theinner tube, its initial wall thickness must be thinner than the initialwall thickness of the inner tube in order to obtain a decrease indiameter proportionate to the inner tube. In this way, the respectivediameters of tubes 12, 14 and their wall thicknesses are reducedproportionately and their lengths increased identically thus minimizingthe chance of delamination.

In the preferred embodiment of FIG. 1, metal cladding tube 12 is madefrom a radiopaque material such as platinum, gold, tantalum, tungsten,platinum-iridium alloy, or palladium. Substrate tube 14 is preferablymade from a material such as stainless steel including 316L, anickel-cobalt-chromium-molybdenum alloy such as MP35N, or from achonichrome such as L605. MP35N is a trade name for a metal alloycomprising 35% nickel, 33.2% cobalt, 20% chromium, 9.53% molybdenum, andtrace amounts of other elements. L605 is a trade name for a metal alloycomprising 50.5% cobalt, 20% chromium, 15.28% tungsten, 9.8% nickel, andtrace amounts of iron and other elements. The aforementioned materialsfacilitate consistent tube diameter and wall thickness reduction whileminimizing the chance of delamination of the concentric tubes. Of coursereversing the material selection for the substrate tube and the claddingtube in specific applications is also contemplated. In addition, asubstrate tube containing a superelastic alloy such as NiTi can also beused.

Laminate tube 10 comprising of metal cladding tube 12 over substratetube 14 is optionally mounted on mandrel 16 and rolled by application ofexternal pinching pressure through roller 18. This is represented in theperspective view of FIG. 1. Along with the rolling operation depicted inFIG. 1, the present invention contemplates a co-drawing or cold drawingoperation shown in the perspective view of FIG. 2. Here, laminate tube10 with metal cladding tube 12 surrounding substrate tube 14 is shownprior to passing through opening 20 of die 22. By passing through aseries of dies 22 with sequentially decreasing opening diameters, it ispossible to deep draw laminate tube 10 to the final desired diameter. Asthe name suggests, this cold drawing process is preferably carried outat room temperature, below the recrystallization temperatures of thetube materials. By repeating the operations shown in FIGS. 1 and 2, itis possible to reduce laminate tube 10 from a starting outside diameterof, for example, about 0.5 inch down to about 0.06 inch. The startingwall thickness for the laminate tube 10 is about 0.03 to about 0.065inches and is reduced down to about 0.003 inch.

In a preferred embodiment process, the rolling and cold drawingoperations are repeated to achieve a maximum of 25 percent in reductionof surface area, to be followed by a heat treating step to release builtup internal stresses. Without the heat treating step, there is apossibility that the deformations are sufficient to exceed the ultimateyield strength of the materials thereby causing ruptures or cracks. Eachsequence of operations slowly reduces the diameter of composite stent 10while proportionately increasing its length.

Although the rolling and cold drawing processes of the present inventionare conducted at room temperature, the pressures involved may cause thetemperature between metal cladding tube 12 and substrate tube 14 toelevate sufficiently to facilitate a mechanical bond which is typicallycreated between the two adjacent layers. In this manner, metal claddingtube 12 is permanently attached to substrate tube 14 and delamination ofthe two materials is minimized under normal operating conditions for thestent. It is desirable to eliminate delamination between the two or morelayers entirely. Preferably, the material used as substrate tube 14 hasa smaller coefficient of thermal expansion than the material used forthe cladding tube 12. This facilitates maintaining contact between thetwo tubes 12 and 14 during the rolling and cold drawing processes andprevents delamination of the tubes subsequent thereto.

In a preferred method, laminate tube 10 undergoes about a twenty-fivepercent (25%) diameter reduction from the rolling or cold drawingoperations. This is accomplished by passing laminate tube 10 through aseries of dies 22 with each die reducing the diameter by preferably onepercent (1%). With a series of twenty-five dies 22, it is possible toachieve the twenty-five percent (25%) diameter reduction.

Laminate tube 10 then undergoes a heat treat process to release stressand to eliminate restrained dislocations. Next, laminate tube 10undergoes another twenty-five percent (25%) diameter reduction by colddrawing or rolling, followed by another heat treating process. Thiscycle is repeated until the desired diameter of laminate tube 10 isreached. Throughout the present invention process, laminate tube 10 mayoptionally undergo anneal cycles in order to impart desired materialproperties such as ductility, strength, etc. Through the presentinvention process, it has been observed that the finished laminate tube10 has a straightness of 0.02 inch per inch for a six to twelve inchlength tube. When the final diameter is reached, the laminate tube iscut to length.

Laminate tube 10 is further processed to form a stent pattern thereinsuch as illustrated by stent 40 in FIGS. 5 and 6 discussed below. Onemethod for forming such a stent pattern is by chemical etching. Such aprocess is disclosed in, for example, U.S. Pat. No. 5,735,893 to Lau etal., entitled “Expandable Stents and Method for Making Same,” thecontents of which is hereby incorporated by reference. Alternatively, astent pattern may be formed by a laser cutting process. Such a processis shown and disclosed in, for example, U.S. Pat. No. 5,759,192 toSaunders, entitled “Method and Apparatus for Direct Laser Cutting ofMetal Stents,” the contents of which is hereby incorporated byreference.

FIG. 3 is a perspective view of a finished laminate tube 24 having metalcladding tube 12 laminated to substrate tube 14. The thickness of asingle wall of the metal cladding tube 12 is about 0.0001 to about 0.010inches, preferably about 0.0005 to about 0.004 inches. The thickness ofa single wall of the substrate tube 14 is about 0.0001 to about 0.010inches, preferably about 0.001 to about 0.004 inches. The material ofthe substrate tube 14 is preferably 316L stainless steel, but can alsobe other types of stainless steel, MP35N, L605 or superelastic alloyssuch as NiTi. The material of the metal cladding tube 12 is preferablyplatinum-10%iridium, but can also be gold, tantalum, platinum,palladium, tungsten or the like.

FIG. 4 provides a perspective view of an alternative embodiment of alaminate tube 28 having substrate tube 30 that is laminated with firstmetallic cladding tube 32. Second metallic cladding tube 34 is laminatedto the outer surface of first metallic cladding tube 32. The thicknessof a single wall of the substrate tube 30 is about 0.0001 to about 0.010inches, preferably about 0.001 to about 0.004 inches. The thickness of asingle wall of the first metallic cladding tube 32 is about 0.0001 toabout 0.002 inches, preferably about 0.0005 to about 0.001 inches. Thethickness of a single wall of the second metallic cladding tube 34 isabout 0.0001 to about 0.002 inches, preferably about 0.0005 to about0.001 inches. The material of the substrate tube 30 is preferably 316Lstainless steel, but can also be other types of stainless steel, MP35N,L605, NiTi or the like or any suitable radiopaque metal such as thosediscussed above. The material of the first cladding tube 32 ispreferably NiTi, but can also be stainless steel, MP35N, L605 or thelike, or any suitable radiopaque metal such as those discussed above.The material of the second metallic cladding tube 34 is preferablyplatinum-10%iridium, but can also be any other suitable radiopaque metalsuch as those disused above, or a superelastic alloy such as NiTi, or ahigh strength metal or alloy such as stainless steel, MP35N, L605 or thelike.

The multiple layers of cladding of laminate tube 28 are created aspreviously described in connection with FIGS. 1 and 2, except thatsecond metallic cladding tube 34 is added to the outside surface offirst metallic cladding tube 32. The three tubes 30, 32, 34 then undergothe rolling or cold drawing, and heat treating operations as describedpreviously. When the final diameter is reached, laminate tube 28 is cutto the desired length and processed to form a stent pattern.

As previously discussed, one typical metallic cladding or substratematerial is superelastic or pseudoelastic nickel-titanium (NiTi) alloy.Because nickel-titanium is a superelastic or shape memory alloy, it ispossible to create a stent that reverts to various formations based onthe ambient temperature and applied stress. In one example, a NiTi-cladstent is formed full size but deformed (i.e., compressed) into a smallerdiameter onto the balloon of a delivery catheter to facilitate transferto the intended intraluminal site. The stress induced by the deformationtransforms the stent from an austenitic phase to a martensitic phase.Upon release of the restraining force, when the stent reaches thedesired site, the stent self-expands isothermally by transformation backto the austenitic phase. Similarly, for shape memory NiTi alloys, themetal transforms from the martensitic to the austenitic phase uponapplication of heat, such as exposure to body temperature, resulting inself-expansion of the cladding material. The behavior of suchsuperelastic alloys and their processing are well known in the art.Certainly a benefit is that the nickel-titanium eases the expansion ofthe stent in normal body temperatures. In a preferred embodiment, if thecladding includes a radiopaque metal such as gold, platinum, tantalum,platinum-iridium alloy, the radiopacity of the stent is improved.Accordingly, the present invention can have enhanced performance orexpansion characteristics as well as improved visibility for thecardiologist.

In FIG. 5 a laminate stent 40 incorporating features of the invention isillustrated mounted on a delivery catheter 41. The laminate stent 40generally has a plurality of radially expandable cylindrical elements 42disposed generally coaxially and interconnected by elements 43 disposedbetween adjacent cylindrical elements. The delivery catheter 41 has anexpandable member or balloon 44 for expanding the laminate stent 40within an artery 45. The artery 45, as shown in FIG. 5, has a dissectedlining 46 which has occluded a portion of the arterial passageway.

A laminate stent 40 can have an outside diameter of up to about 0.1 inchin the unexpanded condition, preferably, about 0.05 to about 0.07inches. The laminate stent 40 can be expanded to an outside diameter ofabout 0.06 to about 0.3 inches or more, preferably about 0.1 to about0.2 inches, when deployed in a body lumen. The length of the laminatestent 40 prior to expansion is about 10 to about 50 mm, preferably about15 to about 25 mm. In addition, multiple laminate stents 40 can beconnected in order to create a stent with an effective length of anymultiple of the previously discussed lengths. Thus, 2, 3, 4, 5 or morelaminate stents 10 can be connected in order to create a stent with alonger effective length.

The delivery catheter 41, onto which the stent 40 is mounted, can beessentially the same as a conventional balloon dilatation catheter usedfor angioplasty procedures. The balloon 44 may be formed of suitablematerials such as polyethylene, polyethylene terephthalate,polyvinylchloride, nylon and ionemers such as Surlyn™ manufactured bythe polymer products division of the DuPont Company. Other polymers mayalso be used. In order for the laminate stent 40 to remain in place onthe balloon 44 during delivery to the site of the damage within theartery 45, the laminate stent 40 is compressed onto the balloon. Aretractable protective delivery sleeve 50 as described in copendingapplications Ser. No. 07/647,464 filed on Apr. 25, 1990 and entitledSTENT DELIVERY SYSTEM may be provided to further ensure that the stentstays in place on the expandable portion of the delivery catheter 41 andprevent abrasion of the body lumen by the open surface of the stent 40during delivery to the desired arterial location. Other means forsecuring the laminate stent 40 onto the balloon 44 may also be used,such as providing collars or ridges on the edges of the working portion,i.e., the cylindrical portion, of the balloon.

Each radially expandable cylindrical element 42 of the laminate stent 40may be independently expanded. Therefore, the balloon 44 may be providedwithin an inflated shape other than cylindrical, e.g., tapered, tofacilitate implantation of the laminate stent 40 in a variety of bodylumen shapes.

In a preferred embodiment, the delivery of the laminate stent 40 isaccomplished in the following manner. The laminate stent 40 is firstmounted onto the inflatable balloon 44 on the distal extremity of thedelivery catheter 41. The balloon 44 is slightly inflated to secure thelaminate stent 40 onto the exterior of the balloon. The catheter/stentassembly is introduced within the patient's vasculature in aconventional Seldinger technique through a guiding catheter 47. A guidewire 48 is disposed across the damaged arterial section with thedetached or dissected lining 46 and then the catheter/stent assembly isadvanced over a guide wire 48 within the artery 45 until the laminatestent 40 is directly under the detached lining 46. The balloon 44 of thecatheter is expanded, expanding the laminate stent 40 against the artery45.

The laminate stent 40 serves to hold open the artery 45 after thecatheter 41 is withdrawn. Due to the formation of the laminate stent 40from an elongated laminate tube, the undulating component of thecylindrical elements of the laminate stent 10 is relatively flat intransverse cross-section, so that when the stent is expanded, thecylindrical elements are pressed into the wall of the artery 45 and as aresult do not interfere with the bloodflow through the artery 45. Thecylindrical elements 42 of the laminate stent 40 which are pressed intothe wall of the artery 45 will eventually be covered with endothelialcell growth which further minimizes bloodflow interference. Theundulating portion of the cylindrical sections 42 provide good trackingcharacteristics to prevent stent movement within the artery.Furthermore, the closely spaced cylindrical elements 42 at regularintervals provide uniform support for the wall of the artery 45, andconsequently are well adopted to tack up and hold in place small flapsor dissections in the wall of the artery 45.

FIG. 6 is an enlarged perspective view of the laminate stent 40 shown inFIG. 5 with one end of the stent shown in an exploded view to illustratein greater detail the placement of interconnecting elements 43 betweenadjacent radially expandable cylindrical elements 42. Each pair ofinterconnecting elements 43 on one side of cylindrical elements 42 arepreferably placed to achieve maximum flexibility for a stent. In theembodiment shown in FIG. 6, the laminate stent 40 has threeinterconnecting elements 43 between adjacent radially expandablecylindrical elements 42 which are 120° apart. Each pair ofinterconnecting elements 43 of one side of a cylindrical elements 42 areoffset radially 60° from the pair on the other side of the cylindricalelement. The alternation of the interconnecting elements result in astent which is longitudinally flexible in essentially all directions.Various configurations for the placement of interconnecting elements 43are possible. In addition, while the expandable cylindrical elements 42and interconnecting elements 43 have been shown in the stent patterndepicted in FIGS. 5 and 6, any suitable stent pattern that allows for adesired amount of expansion and radial strength for a given applicationis also contemplated. For example, the laminate tubes 10, 24 and 28could have any of a number of mesh-like or spiral stent patterns formedthereon.

While particular embodiments of the present invention have beenillustrated and described, it is apparent to those skilled in the artthat various modifications can be made without departing from the spiritand scope of the invention. Any of a variety of stent designs andapplications can benefit from the present invention. Accordingly, it isnot intended that the present invention be limited except by theappended claims.

What is claimed is:
 1. A method of fabricating a stent for implantationwithin a body lumen, comprising the steps of: disposing a first claddingtube about a substrate tube, wherein the first cladding tube is formedfrom a superelastic material; joining the first cladding tube to anoutside surface of the substrate tube; disposing a second radiopaquecladding tube about the first cladding tube, wherein the secondradiopaque cladding tube comprises a radiopaque metal; joining thesecond radiopaque cladding tube to the first cladding tube; and forminga stent pattern in the laminate tube such that the stent pattern isentirely formed of the substrate tube, the first cladding tube, and thesecond radiopaque cladding tube.
 2. The method of fabricating a stentaccording to claim 1, wherein the substrate tube includes a metalselected from the group consisting of stainless steel,nickel-cobalt-chromium-molybdenum alloy, or chonichrome.
 3. The methodof fabricating a stent according to claim 1, wherein the secondradiopaque cladding tube comprises a metal selected from the groupconsisting of platinum, gold, tantalum, tungsten, platinum-iridium, andpalladium.
 4. The method of fabricating a stent according to claim 1,wherein joining the first cladding tube further comprises cold drawingthe laminate tube.
 5. The method of fabricating a stent according toclaim 1, wherein joining the first cladding tube further comprises heattreating the laminate tube.
 6. The method of fabricating a stentaccording to claim 1, wherein joining the first cladding tube furthercomprises cold drawing the laminate tube to bond the first cladding tubeto the substrate tube.
 7. The method of fabricating a stent according toclaim 1, wherein joining the first cladding tube to the substrate tubefurther comprises passing the laminate tube through a series of dies toreduce an outside diameter of the laminate tube by about 25%.
 8. Themethod of fabricating a stent according to claim 1, wherein an insidediameter of the first cladding tube has an interference fit with theoutside surface of the substrate tube.
 9. The method of fabricating astent according to claim 1, wherein forming the stent pattern furthercomprises chemically etching the laminate tube.
 10. The method offabricating a stent according to claim 1, wherein forming the stentpattern further comprises laser cutting the laminate tube.
 11. Themethod of fabricating a stent according to claim 1, wherein the methodfurther comprises heat treating the laminate tube prior to forming thestent pattern therein.
 12. The method of fabricating a stent accordingto claim 1, wherein the method further comprises cold working thelaminate tube.
 13. The method of fabricating a stent according to claim1, wherein the first cladding tube has a wall thickness that is lessthan a wall thickness of the substrate tube.
 14. The method offabricating a stent according to claim 1, wherein the first claddingtube comprises NiTi alloy.
 15. A method of fabricating a stent forimplantation within a body lumen, comprising the steps of: disposing afirst cladding tube about a substrate tube, wherein the substrate tubeis formed from a superelastic material; joining the first cladding tubeto an outside surface of the substrate tube; disposing a secondradiopaque cladding tube about the first cladding tube, wherein thesecond radiopaque cladding tube comprises a radiopaque metal; andjoining the second radiopuque cladding tube to the first cladding tubeto form a laminate tube; and forming a stent pattern in the laminatetube such that the stent pattern is entirely formed of the substratetube, the first cladding tube, and the second radiopaque cladding tube.16. The method of fabricating a stent according to claim 15, wherein thefirst cladding tube includes a metal selected from the group consistingof stainless steel, nickel-cobalt-chromium-molybdenum alloy, andchonichrome.
 17. The method of fabricating a stent according to claim16, wherein the second radiopaque cladding tube comprises a metalselected from the group consisting of platinum, gold, tantalum,tungsten, platinum-iridium, and palladium.
 18. The method of fabricatinga stent according to claim 15, wherein joining the first cladding tubefurther comprises cold drawing the laminate tube.
 19. The method offabricating a stent according to claim 15, wherein joining the firstcladding tube further comprises heat treating the laminate tube.
 20. Themethod of fabricating a stent according to claim 15, wherein joining thefirst cladding tube further comprises cold drawing the laminate tube tobond the first radiopaque cladding tube to the substrate tube.
 21. Themethod of fabricating a stent according to claim 15, wherein joining thefirst cladding tube to the substrate tube further comprises passing thelaminate tube through a series of dies to reduce an outside diameter ofthe laminate tube by about 25%.
 22. The method of fabricating a stentaccording to claim 15, wherein an inside diameter of the first claddingtube has an interference fit with the outside surface of the substratetube.
 23. The method of fabricating a stent according to claim 15,wherein forming the stent pattern further comprises chemically etchingthe laminate tube.
 24. The method of fabricating a stent according toclaim 15, wherein forming the stent pattern further comprises lasercutting the laminate tube.
 25. The method of fabricating a stentaccording to claim 15, wherein the method further comprises heattreating the laminate tube prior to forming the stent pattern therein.26. The method of fabricating a stent according to claim 15, wherein themethod further comprises cold working the laminate tube.
 27. The methodof fabricating a stent according to claim 15, wherein the first claddingtube has a wall thickness that is less than a wall thickness of thesubstrate tube.
 28. The method of fabricating a stent according to claim15, wherein the substrate tube comprises NiTi alloy.